Geochemical and Mineralogical Data from Legacy Mine Land Sites in Central Colorado, 2019 - 2020

This U.S. Geological Survey (USGS) data release contains data from stream water, groundwater/springs, and sediment samples collected from legacy mine land (LML) sites in central Colorado. The sites were selected using a GIS-based approach that integrated regional geological and geochemical datasets with known mine features and satellite data identifying hydrothermal alteration (ASTER) to identify LML-impacted watersheds with low natural background or metal concentrations slightly above aquatic life standards. The central Colorado watersheds selected for preliminary investigation included 1) McNasser Gulch, 2) upper South Fork Lake Creek, 3) Saints John Creek, and 4) Hall Valley (north fork of South Platte River). Reconnaissance sampling of surface water, groundwater, and sediment (August 2019) to identify sources of trace element contamination in each watershed. Follow-up sampling in the Hall Valley watershed (August 2020) provided flow and concentration data for the four largest surface inflows to a headwater pond and additional locations below the pond outlet. Metal loads at these locations were calculated as the product of flow and concentration.